**31st Annual Meeting of the DPS, October 1999**

*Session 55. Dust and Rings Posters*

Poster Group II, Thursday-Friday, October 14, 1999, , Kursaal Center
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## [55.08] Accretion Rates of Ring Particles in the Roche Zone

*K. Ohtsuki (University of Colorado)*

Gravitational accretion of ring particles is characterized
by impact velocity, coefficient of restitution, and a
parameter r_{p}/r_{H}, the ratio of the sum of the radii of
two colliding particles to their mutual Hill radius. Ohtsuki
(1993, Icarus 106, 228) performed orbital integrations
including collisions and gravitational encounters and found
that the probability of accretion dropped rapidly for
r_{p}/r_{H} > 0.7, because the particles overflow their mutual
Hill sphere. Assuming random impact orientation, Canup and
Esposito (1995, Icarus 113, 331) obtained a simple
expression of capture criteria which can approximately
reproduce the above numerical results. However, Ohtsuki
(1993) investigated accretion probability in the Roche zone
only for a limited range of parameters (several values of
r_{p}/r_{H} in the case of particles on circular orbits, and
two different values of r_{p}/r_{H} in the case with
particles' relative random velocity equal to their escape
velocity). To better understand dynamical evolution of
planetary rings in the Roche zone, we examine accretion
probability of colliding particles by three-body orbital
integrations for a much wider range of parameters.
Preliminary results with e=2i (e and i are orbital
eccentricity and inclination of particles) show that the
accretion probability for r_{p}/r_{H}=0.5 - 0.8 is as low as
0.2-0.5 when the random velocity is as large as the escape
velocity, even when the restitution coefficient in normal
direction is as small as 0.1. Thus, more than 50% of
colliding particles fail to accrete when their random
velocity is as large as their escape velocity, unless
collisions are much more dissipative.

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